JP5263532B2 - Combustion control device and combustion control method for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device and a combustion control method for a diesel engine capable of reliably processing NOx and soot when the combustion mode is changed. <P>SOLUTION: In this combustion control method, an ECU 47 controls the oxygen concentration change rate with respect to the oxygen concentration in a combustion chamber 7 and the injection configuration change rate with respect to the timing and amount of the injection of a fuel so that the combustion mode passes a change route C on a map when the combustion mode is changed between a premixed combustion mode and a diffuse combustion mode, and also controls the oxygen concentration change rate and the injection configuration change rate, referring to the detected results of the processing capacity of a DPF 31 and the processing capacity of a LNT 33, and when the soot processing capacity of the DPF 33 is equal to or higher than the first predetermined values (N1, N3, N5) of the DPF processing capacity and the NOx processing capacity of the LNT 33 is less than the first predetermined values (M1, M3, M5) of the NOx processing capacity, corrects the oxygen concentration change rate and the injection configuration change rate so that the combustion mode passes a change route B in which the produced amount of NOx is less than in a change route C and the produced amount of soot is larger than therein. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a combustion control device and a combustion control method for a diesel engine, and more particularly to a combustion control device and a combustion control method for a diesel engine provided in an engine system having a NOx processing device and a soot processing device.

  2. Description of the Related Art Conventionally, an engine system including a NOx processing device for processing NOx contained in exhaust gas from a diesel engine is known. As such an engine system, there is one described in Patent Document 1.

JP 2000-356126 A

  Specifically, Patent Document 1 describes a diesel engine combustion control device that operates an engine in a premixed combustion mode in a low load operation region and operates an engine in a diffusion combustion mode in a high load operation region. Yes. The engine system on which the combustion control device is mounted includes an HC variable catalyst and a λ variable catalyst for treating NOx (nitrogen oxide). The combustion control device controls the oxygen concentration, the fuel injection amount, and the fuel injection timing in parallel when shifting from the diffusion combustion mode to the premixed combustion mode. Further, such a combustion control device changes the HC according to the engine load region when the NOx occluded in the NOx processing device reaches a saturated state, or makes the air-fuel ratio rich, thereby changing the HC fluctuation type. The catalyst or the λ variation type catalyst is to be regenerated.

  However, in the combustion control device, the oxygen concentration and the amount and timing of fuel injection are controlled in parallel while shifting the combustion mode, so the oxygen concentration and the amount of fuel in the combustion chamber continuously change, As a result, oxygen in the combustion chamber becomes excessive and NOx in the exhaust gas increases, or fuel becomes excessive and soot in the exhaust gas increases. And in the apparatus conventionally used, the transition control of the combustion mode is performed without considering the processing capability of the NOx processing device and the soot processing device provided in the exhaust system. That is, in the conventionally used device, the NOx treatment device approaches the saturation state and the processing capacity is lowered, but the oxygen concentration in the combustion chamber is increased and the NOx in the exhaust gas is increased at the transition to the combustion mode. Or, even though the soot treatment device approaches a saturated state and the processing capacity is reduced, the fuel in the combustion chamber is increased to increase the soot in the exhaust. As a result of such control, there has been a problem that NOx and soot in the exhaust gas are released to the atmosphere without being sufficiently treated.

  Therefore, the present invention has been made to solve the above-described problems, and provides a combustion control apparatus and method for a diesel engine that can reliably process NOx and soot when shifting to a combustion mode. For the purpose.

  In order to solve the above-described problems, the present invention is directed to a diesel engine, a NOx substance treatment device for treating NOx contained in the exhaust of the diesel engine, and soot contained in the exhaust of the diesel engine. A combustion control device for a diesel engine provided in an engine system having a soot treatment device, a NOx treatment capability detection means for detecting the treatment capability of the NOx treatment device, and a soot treatment capability for detecting the treatment capability of the soot treatment device By gradually shifting the oxygen concentration in the combustion chamber of the diesel engine and the timing of fuel injection into the combustion chamber according to the change in the engine load with the detection means, the combustion mode of the diesel engine is changed to the combustion chamber of the diesel engine. The fuel is injected into the combustion chamber at the first timing with the oxygen concentration of the fuel as the first oxygen concentration A pre-combustion combustion mode, and a premixed combustion mode in which the oxygen concentration in the combustion chamber is set to a second oxygen concentration lower than the first oxygen concentration and fuel is injected into the combustion chamber at a second timing earlier than the first timing. Combustion control means for transitioning between, the combustion control means combusting through a first transition route on the map when transitioning the combustion mode between the premixed combustion mode and the diffusion combustion mode The oxygen concentration transition rate relating to the indoor oxygen concentration and the injection mode transition rate relating to the timing and amount of fuel injection are controlled, and the soot treatment device is further referred to by referring to the detection results of the NOx processing capacity detecting means and the soot processing capacity detecting means When the soot treatment capacity is equal to or higher than the first predetermined value of the soot processing capacity and the NOx processing capacity of the NOx processing device is less than the first predetermined value of the NOx processing capacity, the oxygen concentration shift rate and the injection The state transition rate is corrected so that the oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the second transition route in which the NOx generation amount is smaller and the soot generation amount is larger than that in the first transition route. It is characterized by becoming.

  According to the present invention configured as described above, the second transition that preferentially suppresses the generation of NOx over the generation of soot when compared with the first transition route when the combustion mode is shifted. By using the route, it is possible to reduce the burden on the NOx processing apparatus whose processing capability is reduced. Therefore, NOx and soot in the exhaust gas are processed by the NOx processing device in which the processing performance is degraded and the soot processing device in which the processing performance is not degraded, but control is performed so that the NOx in the exhaust gas is reduced. Therefore, NOx and soot in the exhaust gas can be reliably processed.

  In the present invention, preferably, the combustion control means refers to the detection results of the NOx processing capacity detecting means and the soot processing capacity detecting means, and the soot processing capacity of the soot processing device is lower than the soot processing capacity first predetermined value. When the processing capacity is less than the second predetermined value and the NOx processing capacity of the NOx processing apparatus is equal to or higher than the second predetermined value of the NOx processing capacity higher than the first predetermined value of the NOx processing capacity, the oxygen concentration transition rate and the injection mode transition ratio are corrected. Thus, the oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the third transition route in which the soot generation amount is smaller than that in the first transition route and the NOx generation amount is large.

  According to the present invention configured as described above, the third transition that preferentially suppresses the generation of soot over the generation of NOx as compared with the first transition route when shifting to the combustion mode. By using the route, it is possible to reduce the burden on the bag processing apparatus having a reduced processing capacity. Therefore, NOx and soot in the exhaust gas are processed by the soot processing device in which the processing performance is degraded and the NOx processing device in which the processing performance is not degraded, but control is performed so that soot in the exhaust gas is reduced. Therefore, NOx and soot in the exhaust gas can be reliably processed.

  Preferably, in the present invention, the soot processing device is a DPF (Diesel Particulate Filter) device, and the soot processing capacity first predetermined value is a value set in advance according to the exhaust temperature in the combustion chamber, and the exhaust temperature It is set to become smaller as the value becomes higher.

  According to the present invention configured as described above, when the exhaust gas temperature is high and the DPF device is regenerated, there is no significant deterioration in fuel consumption, and the soot processing capacity first predetermined value is further reduced. The opportunity to shift the combustion mode through the second transition route can be increased. Thereby, the processing burden of the NOx processing apparatus with low processing capability can be further reduced.

  Preferably, in the present invention, the NOx processing device is an LNT (Lean NOx Trap) device, and the NOx processing capacity second predetermined value is a value set in advance according to the air-fuel ratio, and the higher the air-fuel ratio becomes. It is set to be large.

  According to the present invention configured as described above, the NOx processing capacity second predetermined value is further reduced when the air-fuel ratio of the exhaust gas is low and there is no significant deterioration in fuel consumption when the LNT device is regenerated. Thus, the opportunity to shift the combustion mode through the third transition route can be increased. Thereby, the processing burden of the bag processing apparatus with low processing capability can be further reduced.

  Preferably, in the present invention, the combustion control means is configured to perform main injection and pilot injection before this in each of the diffusion combustion mode and the premixed combustion mode. The injection interval is larger in the premixed combustion mode than in the diffusion combustion mode.

  Preferably, in the present invention, the correction amounts of the oxygen concentration transition rate and the injection mode transition rate in the second transition route are smaller in the state close to the premixed combustion mode than in the state close to the diffusion combustion mode. .

  According to the present invention configured as described above, the correction amount of the oxygen concentration shift rate and the injection mode shift rate can be reduced in a state close to the premixed combustion mode in which the generation of soot and NOx is small. As a result, in the state close to the premixed combustion mode, it is possible to take the same transition form as the first transition route, so that the burden on either the soot treatment device or the NOx treatment device is unilaterally increased. Can be prevented. And thereby, the reproduction | regeneration frequency of a soot processing apparatus or a NOx processing apparatus can be reduced, and the fall of a fuel consumption can be prevented.

  Preferably, in the present invention, the correction amounts of the oxygen concentration transition rate and the injection mode transition rate in the third transition route are smaller in the state close to the premixed combustion mode than in the state close to the diffusion combustion mode. .

  According to the present invention configured as described above, the correction amount of the oxygen concentration shift rate and the injection mode shift rate can be reduced in a state close to the premixed combustion mode in which the generation of soot and NOx is small. As a result, in the state close to the premixed combustion mode, it is possible to take the same transition form as the first transition route, so that the burden on either the soot treatment device or the NOx treatment device is unilaterally increased. Can be prevented. And thereby, the reproduction | regeneration frequency of a soot processing apparatus or a NOx processing apparatus can be reduced, and the fall of a fuel consumption can be prevented.

  Preferably, in the present invention, in the state close to the premixed combustion mode in the second transition route and the third transition route, each correction amount of the oxygen concentration transition rate and the injection mode transition rate is zero.

  Moreover, in order to solve the said subject, this invention processes the soot contained in the diesel engine, the NOx processing apparatus for processing NOx contained in the exhaust of this diesel engine, and the exhaust of the diesel engine A combustion control method for a diesel engine provided in an engine system having a soot processing device for NOx processing, a NOx processing capability detecting step for detecting the processing capability of the NOx processing device, and a soot processing for detecting the processing capability of the soot processing device The diesel engine combustion mode is changed to the diesel engine combustion mode by gradually shifting the oxygen concentration in the combustion chamber of the diesel engine and the timing of fuel injection into the combustion chamber in accordance with the change in the engine load. Fuel is injected into the combustion chamber at the first timing with the oxygen concentration in the chamber as the first oxygen concentration. And a premixed combustion mode in which the oxygen concentration in the combustion chamber is set to a second oxygen concentration lower than the first oxygen concentration and fuel is injected into the combustion chamber at a second timing earlier than the first timing. A combustion control step for transitioning between the combustion mode and the combustion control step so that when the combustion mode is transitioned between the premixed combustion mode and the diffusion combustion mode, the first transition route on the map is taken. The oxygen concentration transfer rate related to the oxygen concentration in the combustion chamber and the injection mode transfer rate related to the timing and amount of fuel injection are controlled, and further, with reference to the detection results in the NOx processing capacity detection step and the soot processing capacity detection step, The oxygen concentration transfer rate when the soot processing capacity of the processing apparatus is equal to or greater than the first predetermined value of the soot processing capacity and the NOx processing capacity of the NOx processing apparatus is less than the first predetermined value of the NOx processing capacity. And the injection mode transition rate are corrected, and the oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the second transition route where the amount of NOx generated is smaller than that of the first transition route and the amount of soot generation is large. It is designed to do this.

  According to the present invention configured as described above, the second transition that preferentially suppresses the generation of NOx over the generation of soot when compared with the first transition route when the combustion mode is shifted. By using the route, it is possible to reduce the burden on the NOx processing apparatus whose processing capability is reduced. Therefore, NOx and soot in the exhaust gas are processed by the NOx processing device in which the processing performance is degraded and the soot processing device in which the processing performance is not degraded, but the control is performed so that NOx in the exhaust gas is reduced. Thus, NOx and soot in the exhaust gas can be reliably processed.

  In the present invention, preferably, in the combustion control step, the soot treatment capability of the soot treatment device is lower than the first predetermined value of the soot treatment capability with reference to the detection results in the NOx treatment ability detection step and the soot treatment ability detection step. When the NOx processing capacity is less than the second predetermined value and the NOx processing capacity of the NOx processing device is equal to or higher than the NOx processing second predetermined value higher than the NOx processing capacity first predetermined value, the oxygen concentration transfer rate and the injection mode transfer rate are The oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the third transition route that is corrected and has a smaller amount of soot generation and a larger amount of NOx generation than the first transition route. .

  According to the present invention configured as described above, the third transition that preferentially suppresses the generation of soot over the generation of NOx as compared with the first transition route when shifting to the combustion mode. By using the route, it is possible to reduce the burden on the bag processing apparatus having a reduced processing capacity. Therefore, NOx and soot in the exhaust gas are processed by the soot processing device in which the processing performance is degraded and the NOx processing device in which the processing performance is not degraded, but control is performed so that soot in the exhaust gas is reduced. Thus, NOx and soot in the exhaust gas can be reliably processed.

  Thus, according to the present invention, NOx and soot can be reliably processed when the combustion mode is shifted.

It is the schematic which shows the engine system to which the combustion control apparatus of the diesel engine by embodiment of this invention was applied. It is a map which shows the fuel-injection mode according to the state of the diesel engine in embodiment of this invention. In embodiment of this invention, it is a graph which shows the target value of the oxygen concentration in a combustion chamber when performing each combustion mode. In embodiment of this invention, it is a graph which shows the relationship between the fuel injection quantity and timing in each fuel injection form transfer rate at the time of the shift of combustion mode. 5 is a map used by the combustion control device according to the embodiment of the present invention when shifting to a combustion mode. 6 is a map showing the relationship between the amount of soot accumulated in the DPF, the exhaust temperature upstream of the DPF, and the transition route to be selected in the embodiment of the present invention. 6 is a map showing the relationship between the NOx occlusion amount of LNT, the air-fuel ratio λ of exhaust, and the transition route to be selected in the embodiment of the present invention. 6 is a map showing the relationship between the NOx occlusion amount of LNT, the air-fuel ratio λ of exhaust, and the transition route to be selected in the embodiment of the present invention. It is a map which shows the relationship between the NOx processing capability, LNT processing capability, and the transfer route selected in embodiment of this invention. It is a map which shows the relationship between the NOx processing capability, LNT processing capability, and the transfer route selected in embodiment of this invention. It is a map which shows the relationship between the NOx processing capability, LNT processing capability, and the transfer route selected in embodiment of this invention. In embodiment of this invention, it is a flowchart which shows a series of processes of ECU when changing combustion mode.

  Hereinafter, a combustion control apparatus for a diesel engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an engine system to which a combustion control device for a diesel engine is applied.

  As shown in FIG. 1, the engine system includes a diesel engine 1 and an intake passage 3 and an exhaust passage 5 extending from the diesel engine 1. The diesel engine 1 is a multi-cylinder diesel engine, and includes a combustion chamber 7, a piston 9 that moves in the combustion chamber 7, and an injector 11 that injects fuel into the combustion chamber 7 at a predetermined timing. An intake valve 13 is provided between the combustion chamber 7 and the intake passage 3, and an exhaust valve 15 is provided between the combustion chamber 7 and the exhaust passage 5.

  The intake passage 3 is provided with an intake throttle valve 17 for adjusting the intake air amount, a compressor 21 of the turbocharger 19 and an intercooler 23 from the upstream side. The intake passage 3 communicates with the intake side of the combustion chamber 7 of the diesel engine 1 via the manifold 25.

  From the upstream side of the exhaust passage 5, the turbine 27 of the turbocharger 19, the oxidation catalyst 29, and a DPF (Diesel Particulate Filter) as a soot treatment device for collecting particulate matter (PM) in the exhaust gas. ) 31 and an LNT (Lean NOx Trap) 33 as a NOx processing device for processing NOx in the exhaust gas. The LNT 33 traps NOx when the air-fuel ratio of the exhaust gas from the diesel engine is lean, and purges NOx when the air-fuel ratio is rich. In this embodiment, LNT is used as the NOx treatment device. However, as the NOx treatment device, an SCR (Selective Catalytic Reduction) catalyst that injects urea into the exhaust and reduces NOx in the exhaust is used. It may be used.

  Further, an EGR passage 35 is provided between the intake passage 3 and the exhaust passage 5. The EGR passage 35 is configured to recirculate exhaust gas from the downstream side of the DPF 31 to the upstream side of the compressor 21 of the turbocharger 19. Specifically, the EGR passage 35 extends from the downstream side of the DPF 31 to between the intake throttle valve 17 and the compressor 21 of the turbocharger 19. The EGR passage 35 is provided with an EGR cooler 37 that lowers the temperature of the exhaust, and an EGR valve 39 that adjusts the recirculation amount of the exhaust.

  The ECU 41 controls intake, exhaust, and fuel injection of the diesel engine 1. Specifically, the ECU 41 controls the intake amount to the diesel engine 1 by controlling the opening degree of the intake throttle valve 17. Further, the ECU 41 controls the amount of EGR returned to the diesel engine 1 by controlling the opening degree of the EGR valve 39. The ECU 41 controls the oxygen concentration in the combustion chamber 7 by controlling the opening degree of the intake throttle valve 17 and the EGR valve 39.

Further, the ECU 41 controls the timing and amount of fuel supplied into the combustion chamber 7 by controlling the injector 11. Specifically, the ECU 41 controls the injector 11 to perform main injection, pilot injection, and post injection. Here, the main injection is a method in which a relatively large amount of fuel is injected into the combustion chamber 7 and the torque is generated by igniting this fuel. Compared with the pilot injection performed before the pilot injection, A small amount of fuel is injected into the combustion chamber 7 to mix the fuel and air. The post-injection is performed when the DPF 31 is regenerated, and fuel is injected into the combustion chamber 7 during the expansion stroke of the diesel engine 1 and unburned fuel is injected into the exhaust passage 5. Then, by supplying unburned fuel to the oxidation catalyst upstream of the DPF 31, the DPF 31 is regenerated. The ECU 41 controls main injection and pilot injection by detecting the crank angle sensor 43 for detecting the crank angle (CA) of the piston 9, the intake pressure sensor 45 for detecting the pressure state of the intake air, and detecting the oxygen concentration of the exhaust gas. An O ₂ sensor 47 for detecting the air flow, an air flow sensor 49 for detecting the flow rate of air flowing into the diesel engine 1, an intake air temperature sensor 51 for detecting the temperature of air flowing into the diesel engine 1, and a depression of an accelerator (not shown) Accelerator opening sensor 53 for detecting the amount (accelerator opening), differential pressure sensor 55 for detecting the differential pressure upstream and downstream of DPF 31, and the temperature of the exhaust gas upstream of DPF 31 in exhaust passage 5 are detected. This is performed based on the detection result of the exhaust gas temperature sensor 57.

  FIG. 2 is a map showing a fuel injection mode corresponding to the state of the diesel engine. As shown in FIG. 2, in the diesel engine 1, two types of fuel injection modes, a diffusion combustion mode and a premixed combustion mode (PCI combustion mode), are switched according to the engine load and the engine speed.

  In the diffusion combustion mode, the ECU 41 performs pilot injection and main injection when the piston 9 is in the vicinity of the top dead center in the compression process of the combustion chamber 7 so that fuel is injected into the combustion chamber 7. To control. Specifically, in the diffusion combustion mode, pilot injection is performed immediately before the piston 9 reaches top dead center, and main injection is performed immediately after the piston reaches top dead center. Are performed in parallel.

  On the other hand, in the premixed combustion mode, the ECU 41 controls the injector 11 so that fuel is injected into the combustion chamber 7 at a timing earlier than in the diffusion combustion mode. In the premixed combustion mode, the pilot injection and the main injection are performed before the piston 9 reaches the top dead center, and the fuel injection is finished before the fuel is ignited. Thereby, before the fuel ignites, the fuel can create a uniform atmosphere, and the equivalent ratio of the fuel and air can be made relatively low to suppress incomplete combustion of the fuel or generation of soot. This premixed combustion mode is used when the engine load is relatively low and the rotational speed of the diesel engine 1 is relatively low because it is necessary to secure time for making the fuel uniform. The ECU 39 switches the fuel injection mode between the premixed combustion mode and the diffusion combustion mode in accordance with the engine load.

FIG. 3 is a graph showing the target value of the oxygen concentration in the combustion chamber when each combustion mode is executed. In this graph, the oxygen concentration transfer rate is shown on the X axis and the oxygen concentration in the combustion chamber is shown on the Y axis. Indicates. As shown in this figure, the oxygen concentration C ₁ when executing the diffusion combustion mode is higher than the oxygen concentration C ₂ when executing the premixed combustion mode. This is because when the diffusion combustion mode is executed, CO, HC, or soot is likely to be generated if the equivalent ratio of oxygen is increased (oxygen is decreased), so that the combustion chamber is controlled by controlling the EGR amount. This is because it is necessary to suppress the incomplete combustion by increasing the concentration of oxygen supplied into the cylinder 7 as compared with the case of executing the premixed combustion mode. Then, when moving from the premix combustion mode to the diffusion combustion mode, along the path L ₁ is gradually increased oxygen concentration in the combustion chamber 7, while, when the transition from the diffusion combustion mode to the premix combustion mode Gradually decreases the oxygen concentration in the combustion chamber 7 along the path L ₁ . When the oxygen concentration transfer rate in the diffusion combustion mode is 0.0 and the oxygen concentration transfer rate in the premixed combustion mode is 1.0, the oxygen concentration transfer rate increases or decreases in proportion to the oxygen concentration in the combustion chamber 7. To do.

  FIG. 4 is a graph showing the relationship between the timing of fuel injection when changing the combustion mode and the change in fuel injection mode, and FIG. 5 is a map used when changing the combustion mode.

  In FIG. 4, the horizontal axis indicates the crank angle (CA) of the piston 9, and the vertical direction indicates the fuel injection amount. As shown in this figure, when the ECU 41 shifts from the diffusion combustion mode to the premixed combustion mode, the pilot injection timing is gradually delayed, and the pilot injection amount is gradually increased so that the pilot injection amount is increased. It approaches the pilot injection amount in the premixed combustion mode. In addition, when shifting from the diffusion combustion mode to the premixed combustion mode, the ECU 41 gradually advances the timing of pilot injection and gradually decreases the pilot injection amount so as to reduce the pilot injection amount to the pilot injection in the diffusion combustion mode. It is designed to approach the amount.

  In the map shown in FIG. 5, the oxygen concentration transfer rate is shown in the X-axis direction, the injection mode transfer rate is shown in the Y-axis direction, and the point (X, Y) = (0, 0) is the diffusion combustion mode. X, Y) = (1, 1) is the premixed combustion mode. Further, as shown in this figure, NOx increases when the amount of oxygen is large (EGR rate is low) and the combustion temperature is high, NVH increases when the diesel engine load becomes high, and Soot indicates that the combustion temperature is high. It increases when the equivalence ratio is high, and HC increases when the combustion temperature is low and the equivalence ratio is high. The ECU 41 selects the optimum transition route from the three transition routes A, B, and C based on the DPF processing capability of the DPF and the LNT processing capability of the LNT, and the diesel engine 1 based on the selected transition route. The combustion mode is shifted between the diffusion combustion mode and the premixed combustion mode. The transition of the combustion mode is controlled by the ECU 39 controlling the injection mode transition rate of the fuel injection mode by the injector 11 based on the oxygen concentration while controlling the oxygen concentration in the combustion chamber 7.

  The transfer route A is a route that shifts the combustion mode by relatively increasing the oxygen concentration in the combustion chamber 7, and is a route that preferentially suppresses the generation of NOx over the generation of soot. The transition route B is a path for shifting the combustion mode by relatively reducing the oxygen concentration in the combustion chamber 7, and is a path that preferentially suppresses the generation of soot over the generation of NOx. The transition route C is a route that controls the oxygen concentration transition rate and the injection mode transition rate in a well-balanced manner and does not increase NOx and soot comprehensively.

  The transition route A is a transition route that corrects the oxygen concentration transition rate and the injection mode transition rate in the transition route C and preferentially suppresses the generation of NOx over the generation of soot. In the vicinity of the premixed combustion mode in the transition route A, the correction amount becomes zero so that the relationship between the oxygen concentration transition rate and the injection mode transition rate is the same as that in the transition route C. On the other hand, in the vicinity of the diffusion combustion mode of the transfer route A, the change amount of the oxygen concentration transfer rate is corrected so as to be significantly larger than the change amount of the injection mode transfer rate.

  The transition route B is a transition route that corrects the oxygen concentration transition rate and the injection mode transition rate in the transition route C and preferentially suppress the generation of soot over the generation of NOx. In the vicinity of the premixed combustion mode in the transition route B, the correction amount is zero so that the relationship between the oxygen concentration transition rate and the injection mode transition rate is the same as that in the transition route C. On the other hand, in the vicinity of the diffusion combustion mode in the transition route B, the amount of change in the injection mode transition rate is corrected so as to be significantly larger than the amount of change in the oxygen concentration transition rate.

  The route for shifting the combustion mode is selected by the ECU 41 comparing the DPF processing capacity and the LNT processing capacity. Here, the DPF processing capacity refers to the ratio of the amount that can be collected to the upper limit of the amount of soot that can be collected by the DPF 31. Based on the detection result of the differential pressure sensor 55, the DPF processing capacity is determined based on the detection result of the current DPF 31. The detected value is the upper limit value of the DPF 31 that can be collected in advance. It is calculated by calculating the ratio of the current amount of soot collected to the amount of soot collected.

  The LNT processing capacity refers to the ratio of the storable amount to the upper limit value of the NOx amount that can be stored by the LNT 33. The LNT processing capacity is obtained by calculating the integrated value (current NOx storage amount) of the value obtained by the ECU 41 sequentially calculating the NOx generation amount from the oxygen concentration in the combustion chamber 7 of the diesel engine 1 as the NOx storage capacity of the LNT 33 determined in advance. It is calculated by subtracting from the upper limit value and further calculating the ratio of the current NOx storage amount to the NOx storage capacity.

  FIG. 6 is a map showing the relationship between the amount of soot accumulated in the DPF, the exhaust temperature upstream of the DPF in the exhaust passage, and the transition route to be selected. It is a map which shows the relationship between the NOx occlusion amount of LNT, the air fuel ratio (lambda) of exhaust, and the transition route which should be selected.

  In FIG. 6, the vertical axis indicates the amount of soot accumulated in the DPF 31, and the horizontal axis indicates the exhaust temperature upstream of the DPF 31. The vertical axis indicates that the amount of soot accumulated on the DPF 31 is higher toward the upper side, that is, the DPF processing capacity is lower, and the amount of soot accumulation on the DPF 31 is lower toward the lower side, that is, the DPF processing capacity is higher. It shows that. The horizontal axis indicates that the exhaust gas temperature is low on the left side, that is, the fuel efficiency is reduced when the DPF 31 is regenerated, and the right side indicates that the exhaust gas temperature is high, that is, the fuel efficiency is decreased when the DPF 31 is regenerated.

When the accumulation amount of soot in the DPF 31 is large and the exhaust temperature is low (region Z ₁ ), the DPF processing capacity is low and the fuel consumption is greatly reduced when the DPF 31 is regenerated. The transition route B is selected so that the fuel is increased with priority given to the generation of soot, and further no significant reduction in fuel consumption occurs. Further, when the accumulation amount of soot in the DPF 31 is smaller than that shown in the region Z ₁ or when the exhaust temperature is high (region Z ₂ ), the processing capability of the DPF 31 is low and the exhaust temperature is lower than when belonging to the region Z _1. Therefore, it is impossible to select the transition route A in which wrinkles increase, and any one of the transition routes B or C other than this can be selected. Further, when the accumulation amount of soot in the DPF 31 is smaller than that shown in the region Z ₂ or when the temperature of the exhaust gas is higher (region Z ₃ ), the processing capability of the DPF 31 is high, and soot is further increased. Since the fuel consumption is not significantly reduced when the DPF 31 is regenerated, any transition route can be selected.

7 and 8 are maps showing the relationship between the NOx storage amount of LNT, the air-fuel ratio λ of exhaust, and the transition route to be selected. 7 and 8, the vertical axis represents the NOx occlusion amount of the LNT 33, and the horizontal axis represents the exhaust air-fuel ratio λ. On the vertical axis, the NOx occlusion amount of LNT33 is increased on the upper side, and the NOx occlusion amount of LNT33 is decreased on the lower side. The horizontal axis indicates that the air-fuel ratio λ is low on the left side and the air-fuel ratio λ is high on the right side. In the map shown in FIG. 7, when any of the transition routes A, B, and C can be selected based on the map shown in FIG. 6, that is, the relationship between the DPF processing capacity and the exhaust temperature is the region Z ₃ of the map shown in FIG. It is used when belonging to. Further, in the map shown in FIG. 8, when the transition route A cannot be selected based on the map shown in FIG. 6, that is, the relationship between the DPF processing capacity and the exhaust temperature is the region Z ₁ or region Z _{2 in} the map of FIG. It is used when belonging to.

First, referring to the map shown in FIG. 7, when the NOx occlusion amount of the LNT 33 is small and the air-fuel ratio is low (region Z ₄ ), the LNT processing capacity is high and the LNT 33 does not significantly decrease fuel consumption. Can be played. Therefore, in this case, the transition route B that preferentially suppresses the generation of soot over the generation of NOx is selected.

Further, when the LNT processing capability is lower than the case indicated by the region Z ₄ or when the air-fuel ratio λ is high (region Z ₅ ), the LNT processing capability and the DPF processing capability are substantially uniform. A transition route C that does not increase in any way is selected.

Further, when the NOx occlusion amount is larger than that indicated by the region Z ₅ and the air-fuel ratio λ is high (region Z ₆ ), the LNT processing capacity is low, and the regeneration of the LNT is accompanied by a significant reduction in fuel consumption. On the other hand, the use of the map of FIG. 7 as described above satisfies the one of the conditions that the DPF processing capacity is high or the exhaust temperature is high, so that NOx generation is given priority over generation of soot. The migration route A that is to be suppressed is selected.

Next, referring to the map shown in FIG. 8, when the NOx occlusion amount of LNT is small and the air-fuel ratio is low (region Z ₇ ), the LNT processing capability is high as in the case of region Z ₄ , and LNT can be regenerated without significantly reducing fuel consumption. Therefore, in this case, the transition route B that preferentially suppresses the generation of soot over the generation of NOx is selected.

Further, when the LNT processing capability is lower than the case indicated by the region Z ₇ or when the air-fuel ratio λ is high (region Z ₈ ), the LNT processing capability and the NOx processing capability are substantially uniform. A transition route C that does not increase in any way is selected. When the map of FIG. 8 is used, since the DPF processing capacity is low or the exhaust gas temperature is low, the transition route A that preferentially suppresses the generation of NOx over the generation of soot is not used. ing.

  In this way, the ECU 41 first selects a transition route based on the DPF processing capacity of the DPF 31 that has a lower regeneration frequency than the LNT 33, that is, has a higher processing capacity than the LNT 33 for the unit operation time, and further increases the DPF processing capacity. If the migration route cannot be selected based on the DPF processing capability, the migration route is selected based on the DPF processing capability and the LNT processing capability.

  FIGS. 9 to 11 are maps for selecting a migration route with reference to the relationship between the DPF processing capability and the LNT processing capability. The series of processing described with reference to FIGS. 6 to 8 is further detailed. This is for explanation. Specifically, in the description with reference to FIGS. 6 to 8, the transition is made by referring to the relationship between the DPF processing capability and the exhaust temperature first, and then referring to the relationship between the LNT processing capability and the air-fuel ratio. Described as selecting a route. On the other hand, in the following description with reference to FIG. 9 to FIG. 11, the description will be further detailed with a focus on the DPF processing capability and the LNT processing capability.

FIG. 9 is a graph showing the relationship between the DPF processing capability and LNT processing capability at a certain exhaust temperature and the selected transition route that may belong to all the regions Z _{1 to} Z ₃ in FIG. The vertical axis represents the DPF processing capacity (soot collection amount), and the horizontal axis represents the LNT processing capacity (NOx occlusion amount). When the relationship between the DPF processing capability and the LNT processing capability belongs to the region Z9, it indicates that the migration route A is selected, and when it belongs to the region Z10, it indicates that the migration route C is selected. If it belongs to Z11, it indicates that the migration route B is selected.

  The region Z9 is defined by a region where the DPF processing capability is equal to or higher than the DPF processing capability first predetermined value and the LNT processing capability is lower than the LNT processing capability first predetermined value. In such a case, since the DPF processing capability is high and the LNT processing capability is low, the transition route A that preferentially suppresses the generation of NOx over the generation of soot is selected.

  The region Z10 is defined by a region excluding the region Z9 among regions where the DPF processing capability is equal to or greater than the DPF processing capability second predetermined value and the LNT processing capability is less than the LNT processing capability second predetermined value. In such a case, the transition route C is selected because both the DPF processing capability and the LNT processing capability have sufficient processing capability.

  The region Z11 is defined by a region where the DPF processing capability is less than the DPF processing capability second predetermined value or the LNT processing capability is equal to or greater than the LNT processing capability second predetermined value. In such a case, since the DPF processing capacity is low or the LNT processing capacity is high, the transition route B that preferentially suppresses the generation of soot over the generation of NOx is selected.

  Then, under the conditions of a certain exhaust temperature and a certain air-fuel ratio shown in FIG. 9, the DPF processing capacity first predetermined value is N1, the DPF processing capacity second threshold is N2, the LNT processing capacity first predetermined value is M1, and the LNT processing. The capability second predetermined value is set to M2.

  FIG. 10 is a graph showing the relationship between the DPF processing capacity and the LNT processing capacity and the selected transition route when the exhaust gas temperature and the air-fuel ratio are high compared to the map shown in FIG. When the DPF 31 is used as the soot processing device, when the exhaust temperature during operation increases, the amount of fuel required to raise the exhaust temperature to a temperature necessary for regenerating the DPF 31 decreases. Therefore, when the exhaust gas temperature is high, the DPF processing capacity first predetermined value that defines the region Z9 is set to N3 smaller than N1. Thereby, the region Z9 expands downward, and the frequency with which the transition route A is selected increases.

Further, when the exhaust temperature during operation is high, the DPF 31 is easily regenerated as described above.
For this reason, when the DPF processing capability is not high, the generation of NOx is preferentially suppressed over the generation of soot, and even if soot increases, the DPF 31 can be regenerated without a significant reduction in fuel consumption. . Therefore, when the exhaust gas temperature during operation is high, the DPF processing capacity second predetermined value that defines the region Z10 in which the transition route C is selected is set to N4 smaller than N2. As a result, the region Z10 extends downward, while the region Z11 narrows in the vertical direction. Then, the frequency with which the migration route C is selected increases, and the frequency with which the migration route B is selected decreases.

  When the LNT 33 is used as the NOx processing device, the amount of fuel required to purge the NOx stored in the LNT 33 increases when the air-fuel ratio during operation increases and approaches a lean atmosphere. Therefore, when the air-fuel ratio is high, the LNT processing capability first predetermined value that defines the region Z9 is set to M2 that is larger than M1, and the LNT processing capability second predetermined value that defines the region Z10 is larger than M3. The region Z11 is narrowed by setting M4. Thereby, since the frequency with which the transition route B is selected is reduced, the NOx in the exhaust can be reliably processed by the LNT 33.

  FIG. 11 is a graph showing the relationship between the DPF processing capacity and the LNT processing capacity and the selected transition route when the exhaust temperature and the air-fuel ratio are low compared to the map shown in FIG. When the DPF 31 is used as the soot processing device, the amount of fuel required to raise the exhaust temperature to a temperature necessary for regenerating the DPF 31 increases as the exhaust temperature during operation decreases. Therefore, when the exhaust gas temperature is low, the DPF processing capacity first predetermined value that defines the region Z9 is set to N5 that is larger than N1. Accordingly, the region Z9 is narrowed upward, and the frequency of selecting the transition route A is reduced, so that the soot in the exhaust can be reliably processed by the DPF 31.

  Further, when the exhaust temperature during operation is lowered, regeneration of the DPF 31 as described above causes a significant reduction in fuel consumption. Therefore, when the exhaust temperature is low and the DPF processing capacity is not high, the DPF processing capacity second predetermined value that defines the region Z10 is set to N6 that is larger than N2 in order to suppress the generation of soot as much as possible. Is done. As a result, the region Z10 narrows upward and the region Z11 expands upward. And the frequency with which the migration route B is selected increases.

  Further, when the air-fuel ratio during operation is lowered, the amount of fuel required to reduce the air-fuel ratio necessary for regenerating LNT 33 is reduced. Therefore, when the air-fuel ratio is low, the LNT processing capacity second predetermined value that defines the region Z11 is set to M6, which is smaller than M2. As a result, the region Z11 extends to the left, and the frequency with which the transition route B is selected increases.

  As described above, in the description with reference to FIG. 6 to FIG. 8, the transition route is selected in two steps so that the NOx processing capability is first referred to and then the LNT processing capability is referred to. As a result of performing these two steps, the NOx processing capacity and the LNT processing capacity are relatively compared as described with reference to FIGS. 9 to 11, and the transition route is determined based on the result. It comes to choose.

  Next, the operation of the engine system will be described. FIG. 9 is a flowchart showing the operation of the engine system. In the drawing and the following description, the symbol “S” indicates “step”.

  When a series of processes starts, the ECU 41 determines in S1 whether or not there is a request for shifting to the combustion mode. This process is performed by the ECU 41 reading the detection result of the accelerator opening sensor 53 and referring to a map as shown in FIG. Then, when the engine speed and the engine load change and these relations shift from the premixed combustion mode region to the diffuse combustion mode region in FIG. 2, the premixed combustion mode is changed to the diffusion combustion mode. It is determined that there was a request for migration. Further, when the engine speed and the engine load change and these relations shift from the diffusion combustion mode region of FIG. 2 to the premixed combustion mode region, the diffusion combustion mode changes to the premixed combustion mode. It is determined that there was a request for migration. And when there exists any transfer request | requirement, ECU41 performs the process after S2.

  In S2, the ECU 41 calculates the DPF processing capacity. This process is performed by the ECU 41 reading the detection result of the differential pressure sensor 55 and subtracting the soot accumulation amount from the pre-stored soot collection amount of the DPF 31. Next, in S <b> 3, the ECU 41 detects the exhaust temperature upstream of the DPF 41 in the exhaust passage 5. This process is performed by the ECU 41 reading the detection result of the exhaust temperature sensor 57.

Next, in S4, the ECU 41 selects a transition route based on the map of FIG. 6, the DPF processing capacity, and the exhaust temperature. In this process, as described above, when the DPF processing capacity is low and the exhaust gas temperature is low (region Z ₁ ), the transfer route B is selected as the transfer route of the combustion mode. In other cases, since either the migration route A or the migration route C can be selected, one migration route is not selected. In S5, the ECU 41 determines whether one transition route is selected. In this process, it is determined that one transition route is selected only when the transition route B is selected in S4.

And if one of the transition route is selected, ECU 41 in S6, the gradual transition of oxygen concentration along the path L ₁ of the map shown in FIG. 3, and gradually the injection mode according to the map shown in FIG. 4 Thus, the combustion mode is shifted along the selected transition route among the plurality of transition routes in the map shown in FIG. Then, the ECU 41 repeatedly executes this process until it is determined in S7 that the transition to the combustion mode has been completed.

  On the other hand, when it is determined in S5 that one transition route is not selected, the ECU 41 calculates the LNT processing capacity in S8. Next, in S9, the ECU calculates the air-fuel ratio λ in the combustion chamber 7. The air-fuel ratio λ is calculated based on the instantaneous NOx occlusion amount, which is the instantaneous NOx occlusion amount, based on the load of the diesel engine 1 estimated from the rotational speed of the diesel engine 1, the exhaust temperature, and the opening of the intake throttle valve. However, this is performed by accumulating these.

Then, ECU 41 in S10, the relationship between DPF capacity exhaust temperature determines whether it belongs to the map of the region Z ₃ in FIG. If it is determined that the relationship between the DPF processing capacity and the exhaust temperature belongs to the region Z ₃ , the ECU 41 determines the transition route based on the map, the LNT processing capacity, and the air-fuel ratio λ shown in FIG. Select and confirm this migration route. And ECU41 performs the process after S6. On the other hand, if it is determined not to belong to the region Z ₃ in S10, the ECU 41 in S12, select the map shown in FIG. 8, LNT processing capability, and the migration routes based on the air-fuel ratio lambda, this transition The route is fixed.

  Thus, when the ratio of the LNT processing capacity to the DPF processing capacity is equal to or greater than a predetermined amount, the ECU 41 increases NOx that can be processed by the LNT and decreases soot, while at the same time shifting to the combustion mode. When it is less than this, the soot that can be processed by the DPF is increased to reduce NOx. And by such control, the transition route at the time of the transition to the combustion mode can be selected based on the DPF processing capacity and the LNT processing capacity, the NOx and soot increased at the time of the transition to the combustion mode are processed, NOx and soot contained in can be reliably processed.

1 Diesel engine 7 Combustion chamber 47 ECU

Claims (10)

Provided in an engine system having a diesel engine, a NOx substance treatment device for treating NOx contained in the exhaust of the diesel engine, and a soot treatment device for treating soot contained in the exhaust of the diesel engine A diesel engine combustion control device,
NOx processing capacity detecting means for detecting the processing capacity of the NOx processing device;
煤 processing capability detection means for detecting the processing capability of the cocoon processing device;
By gradually shifting the oxygen concentration in the combustion chamber of the diesel engine and the timing of fuel injection into the combustion chamber according to changes in the engine load, the combustion mode of the diesel engine is changed to oxygen in the combustion chamber of the diesel engine. A diffusion combustion mode in which the concentration is a first oxygen concentration and fuel is injected into the combustion chamber at a first timing; an oxygen concentration in the combustion chamber is a second oxygen concentration lower than the first oxygen concentration; and Combustion control means for shifting between premixed combustion modes in which fuel is injected into the combustion chamber at a second timing earlier than the first timing,
When the combustion mode is shifted between the premixed combustion mode and the diffusion combustion mode, the combustion control means passes the first transition route on the map so that the oxygen concentration transition rate and the fuel concentration are related to the oxygen concentration in the combustion chamber. Control the injection mode transition rate regarding the timing and amount of injection,
Further, referring to the detection results of the NOx processing capacity detecting means and the soot processing capacity detecting means, the soot processing capacity of the soot processing apparatus is equal to or more than a first predetermined value of soot processing capacity, and the NOx of the NOx processing apparatus When the processing capacity is less than the NOx processing capacity first predetermined value, the oxygen concentration transition rate and the injection mode transition rate are corrected, and the NOx generation amount is smaller than the first transition route and the soot generation amount is larger. The oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the second transition route;
A diesel engine combustion control device.   The combustion control means refers to the detection results of the NOx processing capacity detecting means and the soot processing capacity detecting means, and the soot processing capacity of the soot processing device is lower than the first predetermined value of soot processing capacity. When the NOx processing capacity of the NOx processing apparatus is less than a predetermined value and the NOx processing capacity is equal to or higher than the NOx processing second predetermined value higher than the NOx processing capacity first predetermined value, the oxygen concentration transition rate and the injection mode transition ratio are corrected, 2. The oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through a third transition route in which the amount of soot generation is smaller than that of the first transition route and the amount of NOx generation is large. A diesel engine combustion control device according to claim 1. The soot treatment device is a DPF (Diesel Particulate Filter) device,
2. The diesel engine combustion according to claim 1, wherein the first predetermined value of the soot processing capacity is a value set in advance according to an exhaust temperature in the combustion chamber, and is set to decrease as the exhaust temperature increases. Control device. The NOx processing device is an LNT (Lean NOx Trap) device,
3. The diesel engine combustion control apparatus according to claim 2, wherein the second predetermined value of NOx processing capacity is a value set in advance according to an air-fuel ratio, and is set to increase as the air-fuel ratio increases.   The combustion control means is configured to cause main injection and pilot injection before this in each of the diffusion combustion mode and the premixed combustion mode, and the interval between the pilot injection and the main injection is the diffusion combustion. The diesel engine combustion control device according to claim 1 or 2, wherein the combustion control device is larger in the premixed combustion mode than in the mode.   The correction amount of each of the oxygen concentration transition rate and the injection mode transition rate in the second transition route is smaller in the state close to the premixed combustion mode than in the state close to the diffusion combustion mode. A diesel engine combustion control device according to claim 1.   The diesel according to claim 2, wherein the correction amount of each of the oxygen concentration transition rate and the injection mode transition rate in the third transition route is smaller in the state close to the premixed combustion mode than in the state close to the diffusion combustion mode. Engine combustion control device.   The diesel according to claim 2, wherein the correction amount of each of the oxygen concentration transition rate and the injection mode transition rate is 0 in a state close to the premixed combustion mode in the second transition route and the third transition route. Engine combustion control device. Provided in an engine system having a diesel engine, a NOx treatment device for treating NOx contained in the exhaust of the diesel engine, and a soot treatment device for treating soot contained in the exhaust of the diesel engine A diesel engine combustion control method comprising:
A NOx processing capacity detecting step for detecting the processing capacity of the NOx processing device;
A cocoon processing capacity detection step for detecting the processing capacity of the cocoon processing device;
By gradually shifting the oxygen concentration in the combustion chamber of the diesel engine and the timing of fuel injection into the combustion chamber according to changes in the engine load, the combustion mode of the diesel engine is changed to oxygen in the combustion chamber of the diesel engine. A diffusion combustion mode in which the concentration is a first oxygen concentration and fuel is injected into the combustion chamber at a first timing; an oxygen concentration in the combustion chamber is a second oxygen concentration lower than the first oxygen concentration; and A combustion control step of transitioning to a premixed combustion mode in which fuel is injected into the combustion chamber at a second timing earlier than the first timing,
In this combustion control process, when the combustion mode is shifted between the premixed combustion mode and the diffusion combustion mode, the oxygen concentration transition rate and the fuel concentration are related to the oxygen concentration in the combustion chamber so as to pass through the first transition route on the map. Control the injection mode transition rate regarding the timing and amount of injection,
Furthermore, with reference to the detection results in the NOx processing capacity detection step and the soot processing capacity detection step, the soot processing capacity of the soot processing apparatus is equal to or greater than a first predetermined value of the soot processing capacity, and the NOx processing apparatus When the NOx processing capacity is less than the NOx processing capacity first predetermined value, the oxygen concentration shift rate and the injection mode shift rate are corrected so that the NOx generation amount is smaller than the first shift route and the soot generation amount is The oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through the second transition route,
A combustion control method for a diesel engine characterized by the above.   In the combustion control step, with reference to detection results in the NOx processing capacity detection step and the soot processing capacity detection process, the soot processing capacity of the soot processing device is lower than the first predetermined value of the soot processing capacity. 2 When the NOx treatment capacity of the NOx treatment device is equal to or higher than the second predetermined value of NOx treatment higher than the first predetermined value of NOx treatment capacity, the oxygen concentration transition rate and the injection mode transition rate are corrected. The oxygen concentration transition rate and the injection mode transition rate are controlled so as to pass through a third transition route that has less soot generation amount and more NOx generation amount than the first transition route. A combustion control method for a diesel engine according to claim 9.

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